This invention relates to a method for forming a multiple pole coupling disc of the type used in an electromagnetic coupling such as an electromagnetic clutch or brake. The coupling disc may be part of a rotary or non-rotary field or may be a rotary or non-rotary armature.
A typical electromagnetic coupling is disclosed in Silvestrini et al U.S. Pat. No. 4,187,939 and, in that particular case, the coupling is an electromagnetic clutch having a rotary armature disc made of magnetic material such as steel and having a field with a rotary coupling disc or rotor which also is made of magnetic material. When the coil of the field is excited, magnetic flux threads a path between the rotor and the axially opposing armature and attracts the armature into engagement with the rotor to couple the two for rotation in unison.
In the coupling disclosed in the Silvestrini et al patent, the armature is formed with a ring of angularly spaced "banana" slots while the rotor is formed with two concentric rings of angularly spaced banana slots located on opposite sides of the ring of slots in the armature. The banana slots form high reluctance air gaps causing the rotor and armature to define four magnetic poles which increase the torque of the coupling. By forming an additional ring of slots in each of the rotor and armature, the coupling may be constructed as a six-pole coupling with even higher torque capacity.
The banana slots conventionally are stamped in the rotor and armature. Presently available stamping techniques dictate that, as a general rule, the radial width of the slots must be at least as great as the thickness of the disc. As a result, difficulty is encountered in stamping multiple rings of slots in a comparatively thick disc which is relatively small in diameter. In addition, adjacent banana slots are separated by magnetic webs or bridges which inherently form low reluctance flux leakage paths extending radially between the poles.
As an alternative to slotting the rotor and armature to form high reluctance air gaps, channels may be machined in the disc and then filled with non-magnetic material to define high reluctance barriers between the poles. Subsequently, the disc is machined to remove the bottoms of the magnetic channels and eliminate the flux leakage paths which otherwise would be created across the bottoms of the channels. This manufacturing process is relatively expensive and becomes even more so when each disc is formed with two or more high reluctance rings.